Synthesis and characterization of various block copolymers prepared by atom transfer radical polymerization

Abstract

A series of well-defined comb-coil block copolymers polystyrene-b-(poly(2-(2-bromopropionyloxy)styrene-g-poly(methylmethacrylate)) (PS-b-(PBPS-g-PMMA))s were synthesized by atom radical transfer radical polymerization (ATRP) with various chain length of coil block and side chains in comb block. The linear diblock copolymers consisting of initiating sites on a specific block was obtained by ATRP of 4-acetoxystyrene, followed by activators regenerated by electron transfer (ARGET) ATRP of styrene. Subsequently, Poly(4-acetoxy styrene) (PAS) was transformed into the functionalized ATRP initiating site block through deacylation and esterification. Grafting of PMMA via ATRP with various chain lengths yielded the desired complex architecture. The phase separation behaviors of resulting polymers were studied with Differential Scanning Calorimetry (DSC), Synchrotron Small-angle X-ray scattering (SAXS), Scanning Electron Microscope (SEM) and Transmission Electron Micrograph (TEM). Depending on molecular weight of each block of the morphologies of PS-b-PBPS diblock copolymers was showed lamellae and hexagonally packed cylinder. The comb-coil block copolymer PS-b-(PBPS-g-PMMA)s also exhibited different phase separation depending on the volume fraction of PMMA and PS. Another comb coil block copolymer, polystyrene-b-((poly(2-(2-bromopropionyloxy)2-ethylacrylate)-g-poly(methyl methacrylate)) (PS-b-(PBPEA-g-PMMA))s whose grafted backbone (i.e., polystyrene vs. polyacrylate) is different. The tendencies of phase separation behavior of PS-b-(PBPEA-g-PMMA)s was similar indicating that the chemical structure of backbone didn't significantly affect to microphase separation. Well-defined star-shaped architectures diblock copolymers, $[poly(methylmethacrylate)-b-poly(3-(trimethoxysilyl propyl methacrylate))]_4$ $[PMMA-b-PTMSPMA]_4$ s were prepared by ATRP. The hydrophobic core PMMA was synthesized via ATRP using 4-arm initiator. Subsequently, PTMSPMA was obtained by ATRP from PMMA macroinitaor, leading to the formation of star-shaped diblock copolymer $[PMMA-b-PTMSPMA]_4$ . The resulting polymers in solution showed the behavior of unimolecular micelle was demonstrated by dynamic light scattering (DLS). Further, organic/inorganic hybrid nanoparticles with PMMA core and PTMSPMA shell having silsesquioxane networks were prepared by base-catalyzed sol-gel process. Characterization of synthesized polymers was confirmed by GPC, 1H NMR. Also, monodisperse hybrid nanoparticles were observed by SEM. Well-defined block copolymer containing amino acid, poly(2-hydroxyethyl methacrylate-L-lysine)-b-poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methyacrylate] [poly(HEMA-L-lysine)-b-poly(OEGMA-co- $MEO_2MA$ )] was synthesized via ATRP. Esterification and condensation with HEMA and Boc-L-lysine produced the monomer of vinyl(Boc-L-lysine-HEMA). Block copolymer poly(HEMA-L-lysine)-b-poly(OEGMA-co- $MEO_2MA$ ) having narrow polydispersity was prepared by sequential random copolymerization of OEGMA and $MEO_2MA$ via ATRP from macroinitiator, and subsequently deprotection of Boc groups in poly(BOC-L-lysine-HEMA). The resulting block copolymers applied chiral selectivity in D,L-lysine mixture that preferentially separated for L-lysine and exhibited enantiomeric excess (80%). The block copolymers absorbing L-lysine were separated by thermoresponsive poly(OEGMA-co- $MEO_2MA$ ) blocks which were aggregated above lower critical solution temperature (LCST).